1. Unify all numbers under double type
A bit lazy, but is easily maintainable. Precision is enough for most use cases.
2. Add more functions
Add `num`, `parselit`, `str`.
3. Fix hex parser error
Previously the "0x" was greedy and matches single zeros, which then raised a parsing error because it couldn't match a hex number.
Reviewed-on: #4
XN grammar and transformation engine are updated, including support for bitwise operations, improved function parameter handling, and enhanced error reporting.
Reviewed-on: dominic/XNeedle#2
